How to force iPhone 4 running iOS 6.0 Not to change orientation

Use the orientation lock.

 

I use rotation inhibitor (with sbsettings)

There is a stock option but unfortunately, that only locks it in portrait mode

 

Here's how to do it, jailbreak not required.

There's bunch of other tips you can do on this page as well:

http://www.apple.com/iphone/tips/

 

Google or Apple Knowledge Base is always the 1st place to inquire